At present there is no vaccine available in the world for prophylaxis or treatment against Zika virus infections. Therefore, there is no prior art relevant to the invention disclosed in this application. However, for general understanding of the background and objectives behind this invention, the invention is discussed hereinafter in below paragraphs.
The Inventors of this patent application anticipated the epidemic potential of Zika virus in regions with high prevalence of Aedes mosquitoes, particularly Aedes aegypti that transmits the virus. The interest in initiating the Zika vaccine project early on, several months before the causal link of Zika virus infection to Guillain Barre Syndrome and to microcephaly became public knowledge in December 2015, was that there was no preparedness in any country in the world, nor measures initiated by anyone at that time to develop a vaccine to stop the ongoing virus transmission in countries such as Brazil, and to prevent further transmission in countries at risk for Zika virus. Increased International travel to and from regions with ongoing virus transmission impose a major risk to initiate an outbreak in countries with high prevalence of Aedes mosquitoes, particularly Ae. aegypti and those having a large naïve population hither to unexposed to the virus. The clinical picture of Zika virus infection in the early stages with characteristic high fever, maculopapular rashes and arthralgia is strikingly similar to the early onset symptoms of Chikungunya and Dengue virus infections that make differential diagnosis particularly challenging.
Zika virus vaccine project was initiated at the time when very little or no information was available on virus pathogenesis, genetic diversity, transmission, diagnosis, serological correlates for protection or animal models to test the vaccine concepts. From vaccine point of view, there was no information on whether the virus can be cultured in vitro in cell substrates and if yes, which cell substrates are best suitable, mechanism of adaptation to cells, potential virus titers and the feasibility to manufacture the vaccine product for human administration, as the published information at that time pertained to passaging the virus in mouse brain which is not suitable for vaccine production. Bharat Biotech initiated steps to start Zika vaccine project in late 2014, and commenced the experimental work soon thereafter resulting into this said patent application.
Arbovirus (arthropod-borne) infections are caused by viruses that are spread by arthropods such as mosquitoes. They cause significant human illness ranging from mild, asymptomatic infection to acute encephalitis or hemorrhagic fever that can prove fatal. The most significant arboviruses causing human illness belong to three viral families, Togaviridae, Flaviviridae, and Bunyaviridae. Arbovirus infections are rampant in developing countries and cause severe morbidity particularly in the elderly population. The common characteristic feature of arbovirus infections caused by Dengue, Chikungunya, Zika, Japanese encephalitis and West Nile viruses among others is fever, headache, myalgia, joint pains with swelling and maculopapular rashes during the acute phase of the viral infection. Arthralgia is particularly a characteristic feature of Chikungunya, Dengue and Zika virus fever. Co-infections are common as the arboviruses largely share the same mosquito vectors such as for example Dengue, Chikungunya and Zika viruses that are transmitted by Aedes mosquitoes. Japanese encephalitis virus and West Nile viruses are transmitted predominantly by Culex mosquitoes. The problem is acute in developing countries where mosquito vector control programs have been ineffective and largely unsuccessful. The problem is compounded by the fact that there are no robust diagnostic methods available for diagnosing the disease causing viruses with certainty. International travel has aided widespread dissemination of these infectious agents, and diseases like Dengue and Chikungunya hitherto confined to tropical countries are now spread geographically to new areas and to temperate regions. Zika virus is reportedly spread to over 65 countries in the last two years. Autochthonous epidemic outbreaks reported in few countries in these regions are sustained by the local population of mosquito vectors.
Zika virus (ZIKV) is an emerging zoonotic arbovirus, belonging to the Flaviviridae family. Like Dengue and Chikungunya viruses, Zika virus can also be transmitted by Aedes mosquitoes more specifically A. furcifer, A. taylori, A. luteocephalus, A. africanus. A. albopictus and predominantly by, A. aegypti. Travel tourism to nations where the recent epidemics were reported such as Polynesia has aided the geographical spread of the virus infection to Brazil, Columbia, Italy and to other countries. An autochthonous outbreak of the virus was reported in Italy caused by the locally established Aedes mosquitoes. In Asia, Zika virus infection has occurred sporadically in Cambodia, Thailand, Indonesia, Malaysia and Bangladesh although large epidemic outbreaks have not been reported in these regions.
Chikungunya virus (CHIKV) is an Alphavirus of the family Togaviridae. The virus causes self-limiting febrile infection characterized by acute onset of high fever, headache, myalgia, arthralgia, swelling in joints and maculopapular rashes. Severe symptoms such hemorrhagia, fulminant hepatitis and neurological symptoms were reported in the more recent epidemics. Chikungunya virus is transmitted by both the Aedesaegypti and Aedes albopictus mosquitoes. Japanese encephalitis virus (JEV) is also a flavivirus of the family Flaviviridae and is transmitted largely by the Culex mosquitoes. JEV is related to Dengue, Yellow fever virus, Zika and West Nile viruses. JEV infection is largely asymptomatic, but in general it causes malaise with fever, headache and other flu-like symptoms. Rarely, the clinical infection progresses to encephalitis with seizures, spastic paralysis, coma and death. Children are particularly susceptible. In the countries endemic for JEV, most adults have natural immunity after childhood infection. Adults not exposed to the infection during childhood are susceptible at any age. The case-fatality rate in JEV caused by encephalitis can be as high as 30%. Neurological complications or psychiatric sequelae occur in high proportion of the cases with encephalitis. Globally, about 3 billion population is at risk for JEV infection. A few vaccines for prophylaxis of JEV infection have been successfully commercialized. Dengue virus (DENV) is a member of Flaviviridae family. The arbovirus infections can no longer be considered region specific as they are now geographically widespread and are significant public health problem in many parts of the world. The morbidity caused by the aforementioned arbovirus infections is usually high, and arthralgia in particular, adversely impacts physical mobility of the patients. Zika virus causes more serious congenital birth deformities during infection in pregnancy, and Zika related Guillain Barre syndrome have been confirmed in the ongoing epidemics. Like any other viral infections, no specific therapeutics is available. Prophylactic vaccination can effectively interrupt Zika virus transmission and a vaccine would be the front line of defense from the Zika virus disease.
With this in mind, an effective strategy was developed to prevent further transmission of Zika virus to protect naïve population in countries with ongoing epidemics and in countries where active Zika virus transmission has not been reported as yet. A combination vaccine for arbovirus infections is good strategy to protect vulnerable population from debilitating illnesses caused by Dengue, Chikungunya, Zika, Japanese encephalitis, West Nile and Yellow Fever viruses. Vaccines for JEV, Yellow Fever and one for Dengue serotypes has been commercialized and those for West Nile and CHIKV are in clinical development. There is no vaccine for Zika virus infection as yet, and the current invention discloses the methods for development of the first candidate Zika vaccines.
However, the choice of antigens to include in such a vaccine kit depends on several factors. The antibody dependent enhancement of virus caused by the Dengue serotypes is well researched and published and so also the cross reactivity of flavivirus antibodies. But what was not clear is that if there would be such interference or cross reactivity of prevalent Chikungunya antibodies in the same population that is affected by Zika virus. Similarly, it was not known if antibodies to Japanese encephalitis virus could cause antigenic interference in developing immunity to Zika virus and it was an interesting thought to study the same. The proposed work provides an insight to any possible immune interference caused by prevalent JE and CHIKV antibodies to candidate Zika vaccine.
In the current invention, candidate Zika virus vaccines have been developed and tested for potency with various formulations to elicit the appropriate level of immune response to protect against Zika virus disease. As there was no significant antigenic interference to Zika induced immune response by Japanese encephalitis virus vaccine and Chikungunya virus vaccine when co-administered or combined as a combination vaccine, the formulations were effective in eliciting high level of neutralizing antibodies capable of conferring protection against each of the viruses.